Traditional offset printing use the theory that dampening liquid cannot mix with ink, nature of the patterned area on the printing plate is hydrophobic and has affinity to ink, so as to print ink onto this area. The non-patterned area on the printing plate is coated with a thin dampening liquid film, which is hydrophilic and is repellent to ink. Thus, the non-patterned area not be covered by the dampening liquid will not be printed by ink, and there is no dampening liquid film on printed area. In order to let the dampening liquid film smoothly formed, the surface tension of water need to be reduced. Therefore in the nowadays offset printing technique, ethanol, Isopropyl Alcohol (IPA), ether or other substituting agent has to be added to the dampening liquid to reduce the water surface tension.
However, there are many disadvantages of ethanol, IPA, ether or other substituting agent: 1. IPA is a harmful material with high volatility, no matter it is emitted to the air or to the nature, it will have pollution to environment, especially in a relatively close printing workshop, the volatilized IPA vapor will be seriously harmful to human's health; 2. Ethanol & IPA are flammable, their flash point is so low that they can easily burn or explode, so they are extremely unsafe; 3. Increase printing operational cost; 4. Causing many printing problems, since ethanol, IPA, ether or other substituting agent can dissolve and dilute ink, the ink at the boundary between the ink surface and water surface will be easily erode and incur printing problems such as poor ink drying, ink nebulization, ink's pile up, ink easily pull out, ink fading, etc.
Over the years, people have tried to improve the formulation of ink or dampening liquid so as to solve the above-mentioned problems. For example, they have tried to change the formulation of ink to enhance its resistance to the dampening liquid erosion, or to change the formulation of the dampening liquid to reduce its erosion to ink, wherein the later is getting more interest of the people. With a growing concern and attention of humans on the environment, health, safety, people's research turn into the use of ethanol or isopropyl alcohol substituting agent to reduce or even eliminate the percentage of ethanol or isopropyl alcohol in the dampening liquid. In domestic and international, now people are adding substituting agents of ethanol (these substituting agents all belong to alcohols or ethers substances, such as propylene glycol, ethylene glycol, diethylene glycol, propylene glycol methyl ether, etc.) into the dampening liquid, so as to replace ethanol or isopropyl alcohol (IPA). But these substituting agents can not completely replace ethanol or isopropyl alcohol (IPA). Thus, some so-called “non-alcohol” dampening liquids containing these substituting agents cannot be totally free of alcohol, actually they generally have an alcohol content of at least 5 wt %.
Furthermore, these substituting agents are expensive, apart from the increase of printing cost, they still cannot solve the problems such as ink erosion, environment pollution, health harm, etc., For example, the substituting agent to alcohol and ether has more erosion to ink and incur to more problems than ethanol during the printing operation, such as poor ink drying, ink fading, ink nebulization, ink's pile up, ink easily pull out, and poor color control, etc.
Currently in the offset printing technology field, people are willing to invent or innovate an absolute zero alcohol offset printing system (i.e., the dampening liquid in this offset printing system is totally free of alcohol), so as to solve above long lasting problems.
The present invention uses a different approach to solve the above technical problems, and firstly proposes a zero alcohol offset printing system in the domestic and international level and successfully implements it.